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400          COLZA OIL AND OTHER CRUCIFEROUS OILS

its critical solubility temperature in alcohol determined. For this purpose
the liquid acids are dissolved in 40 c.c. of absolute alcohol, the solution
being heated gently, treated with slight excess of saturated sodium car-
bonate solution, evaporated almost to dryness and dried in a vacuum over
sulphuric acid. The dry residue is powdered and purified from, the excess
of admixed sodium carbonate by successive treatments with 50,40 and 30
c.c. of absolute alcohol, with which it is heated to boiling on a water-bath.
The liquids are filtered hot and the sodium soap separated by cooling as
a white or straw-yellow, caseous mass, which is pumped off and dried in a
vacuum over sulphuric acid. Of the perfectly dry, powdered sodium soap,
0-5 gram is treated in a large test-tube with 20 c.c. of absolute alcohol, the
tube being hung in a beaker full of water and a thermometer introduced
so that its bulb is in the centre of the liquid.

The liquid is then heated and continually stirred with the thermometer
until a clear solution is obtained, the whole being then allowed to cool spon-
taneously. At a certain point the alcoholic solution in the test-tube is
seen to contain minute crystals, which are only barely noticeable at first,
but rapidly multiply and fill the whole mass of the liquid. The temperature
at which the first crystals are observed is the characteristic critical tem-
perature.

When the crystallisation is well under way, the thermometric column
remains stationary for some time, or at least falls with greatly increased
slowness.

The sodium soap of the liquid fatty acids of colza oil has the critical solu-
bility temperature in alcohol, 50-45 ; for other seed oils and for olive oil this
temperature is lower (see later). Further, the sodium soaps of olive oil and
of various seed oils are deposited with a caseous, flocculent and glutinous appear-
ance, whereas that of olive oil, at least at first, is distinctly crystalline.

From the melting point and iodine number of the solid fatty acids and the
critical solubility temperature of the sodium soap of the liquid acids, colza (or
ravison) oil may be detected and approximately estimated in its mixtures with
other oils ; the following data are given by Tortelli and Fortini :

Oils.
	Melting Point
	Iodine Number
	Critical Solubility Temperature of


	Solid Acids.
	of Solid Acids.
	the Sodium Soap of the Liquid


	
	
	


	
	
	

Olive oil     ...... Colza oil, 50 )
	41  42 58-59
	62 7-3
	50-45 24-20

Olive oil, 50 j
	47 4
	32
	4-35

Colza oil, 30 )
	
	
	

Olive oil, 70 J
	
	28
	35-3

Colza oil, 20 )
	
	
	

Olive oil, 80 j
	50-51
	22
	35-3


	
	
	

Olive oil, 90 j
	54-55
	12-8
	


	
	
	


	55-56
	9-2
	20-18

Cottonseed oil .....
	57-58 57-58
	13 19
	22-18 16-14

into the lower part of the bulb.   The iodine number is